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| 型号： | LM3445TRIACEVAL |
| 厂商： | National Semiconductor |
| 文件页数： | 21/40页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL LM3445MM |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| 电流 - 输出 / 通道： | 770mA |
| 输出及类型： | 1，非隔离 |
| 特点： | 可调光 |
| 输入电压： | 8 ~ 12V |
| 已供物品： | 板 |
| 已用 IC / 零件： | LM3445MM |
| 相关产品： | LM3445MMX-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMDKR-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMCT-ND - IC LED DRIVER TRIAC DIMM 10-MSOP LM3445MMTR-ND - IC LED DRIVER TRIAC DIMM 10-MSOP |
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SNVS570L – JANUARY 2009 – REVISED MAY 2013
The input voltage to the buck converter (V BUCK ) changes with both line variations and over the course of each
half-cycle of the input line voltage. The voltage across the LED string will, however, remain constant, and
therefore the off-time remains constant.
The on-time, and therefore the switching frequency, will vary as the V BUCK voltage changes with line voltage. A
good design practice is to choose a desired nominal switching frequency knowing that the switching frequency
will decrease as the line voltage drops and increase as the line voltage increases (see Figure 26 ).
1.50
Series
connected LEDs
1.25
1.00
3 LEDs
5 LEDs
0.75
0.50
7 LEDs
9 LEDs
0.25
0
50
100
150
200
V BUCK (V)
Figure 26. Graphical Illustration of Switching Frequency vs V BUCK
The off-time of the LM3445 can be programmed for switching frequencies ranging from 30 kHz to over 1 MHz. A
trade-off between efficiency and solution size must be considered when designing the LM3445 application.
The maximum switching frequency attainable is limited only by the minimum on-time requirement (200 ns).
Worst case scenario for minimum on time is when V BUCK is at its maximum voltage (AC high line) and the LED
string voltage (V LED ) is at its minimum value.
V LED(MIN)
t ON(MIN) = K u V
1
BUCK(MAX)
1
f SW
(12)
The maximum voltage seen by the Buck Converter is:
V BUCK(MAX) = V AC-RMS(MAX) x 2
(13)
INDUCTOR SELECTION
The controlled off-time architecture of the LM3445 regulates the average current through the inductor (L2), and
therefore the LED string current. The input voltage to the buck converter (V BUCK ) changes with line variations and
over the course of each half-cycle of the input line voltage. The voltage across the LED string is relatively
constant, and therefore the current through R4 is constant. This current sets the off-time of the converter and
therefore the output volt-second product (V LED x off-time) remains constant. A constant volt-second product
makes it possible to keep the ripple through the inductor constant as the voltage at V BUCK varies.
Copyright ? 2009–2013, Texas Instruments Incorporated
Product Folder Links: LM3445
21
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3445TRIACEVAL/NOPB | 制造商:Texas Instruments 功能描述:TRIAC Dimmable Offline LED Driver Evaluation Board |
| LM3447 | 制造商:TI 制造商全称:Texas Instruments 功能描述:Phase Dimmable, Primary Side Power Regulated PFC Flyback Controller for LED Lighting |
| LM3447-A19-120VEVM | 功能描述:LED 照明开发工具 LM3447 Eval Mod RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| LM3447-A19-230VEVM | 功能描述:LED 照明开发工具 LM3447 Eval Mod RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| LM3447MT | 制造商:TI 制造商全称:Texas Instruments 功能描述:a Phase-Dimmable, Primary-Side Regulated LED Driver |
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